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Bronze Leaf Disease Poses a Threat to Aspen Breeding

Photo of Hybrid aspen leaves showing bronze leaf disease. Mike Ostry, USDA Forest ServiceHybrid aspen leaves showing bronze leaf disease. Mike Ostry, USDA Forest ServiceSnapshot : Bronze leaf of hybrid aspen is a systemic disease that results in a characteristic dark purple to brown pigmentation of infected aspen leaves in late summer. Branches on affected trees die over a period of several years until entire trees eventually die. Many otherwise promising hybrids and natural hybrids are highly susceptible, which suggests that this disease is an important ecological natural genetic barrier that maintains pure aspen species. Forest Service scientists have studied and characterized the complete life cycle, pathology, and host range of this fungus, which were previously unknown.

Principal Investigators(s) :
Ostry, Michael E. 
Research Location : Minnesota
Research Station : Northern Research Station (NRS)
Year : 2013
Highlight ID : 489


Since the mid-1950s, bronze leaf, a disease caused by the fungus Apioplagiostoma populi, has damaged and killed aspen hybrids in plantations and landscape plantings in the Midwest, Northeast, and Canada. Promising hybrids have been eliminated from future planting because of their susceptibility. The disease is common among naturally occurring hybrid trees of seed origin on disturbed sites such as roadsides and railway and power line right-of-ways. Before Forest Service scientists studied this fungus, its complete life cycle, pathology, and host range were unknown. The fungus cannot be grown on artificial media and produces a toxin involved in the disease syndrome. The scientists identified a second spore stage involved in the fungus life cycle and found evidence suggesting that only aspen hybrids, not pure species, are susceptible. The unique pathogen acts as a genetic barrier to natural hybridization among several native and introduced aspen and poplar species, thus preserving the pure species in nature and acting as an obstacle to breeding in aspen improvement efforts.

Forest Service Partners

External Partners

  • M.J. Moore, N.A. Anderson, St. Paul, MN
  • University of Minnesota, Iowa State University

Program Areas